1. Field of the Invention
The present invention relates generally to the control of a hybrid electric vehicle, and more particularly to a method for inhibiting stalling of an engine of a hybrid electric vehicle.
2. Background Art
Hybrid electric vehicles have drivetrains adapted to provide torque to one or more vehicle traction wheels. A drivetrain may include a torque converter and a transmission. The torque converter transfers engine torque to an input shaft of the transmission. The transmission transmits torque to the traction wheels to propel the vehicle.
The applicant of the present invention has discovered that when a hybrid vehicle drivetrain is configured without a torque converter, the engine may experience increased load forces that impede engine rotation. These load forces will stall the engine if they exceed the engine torque. In addition, the load forces are transferred to the engine more rapidly in the absence of a torque converter. As a result, there is less time to predict and prevent engine stalling, such as by increasing engine speed and torque to brace for the anticipated load forces. An electrical machine, such as a starter-alternator, may be used to provide torque to the engine. However, the applicant has discovered that an electrical machine can rapidly consume power and deplete a power source in the absence of an intelligent method of control.
Before applicant's invention, there was a need for an improved method of inhibiting engine stalling in the drivetrain of a hybrid electric vehicle, and more particularly in a drivetrain that does not employ a torque converter. In addition, there was a need for a control methodology that intelligently inhibits engine stalling and reduces depletion of a power source. Problems associated with the prior art is noted above and other problems are addressed by the Applicant's invention as summarized below.